Blocked mercaptosilane coupling agents, process for making the uses in rubber

ABSTRACT

The invention relates to sulfur silane coupling agents containing multiple blocked mercapto groups which are in a state of reduced activity until activated. The coupling agents are advantageously used in rubber formulations, for example, for fabricating tires with low rolling resistance.

The present application is a continuation of copending U.S. patentapplication Ser. No. 12/820,198 filed on Jun. 22, 2010, which is adivisional of U.S. patent application Ser. No. 11/647,780 filed on Dec.22, 2006 and now issued as U.S. Pat. No. 7,781,606, to which priority isclaimed and which is herein incorporated by reference in its entirety.

The present application is directed to an invention which was developedpursuant to a joint research agreement wherein the meaning of 35 U.S.C.§103(c). The joint research agreement dated May 7, 2001 as amended,between Continental AG, and General Electric Company, on behalf of GEAdvanced Materials, Silicones Division, now Momentive PerformanceMaterials Inc.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to the following applications, filedon even date herewith, with the disclosures of each the applicationsbeing incorporated by reference herein in their entireties:

Application Ser. No. 11/617,683, filed Dec. 28, 2006, entitled “TireCompositions And Components Containing Silated Cyclic CorePolysulfides”.

Application Ser. No. 11/617,649, filed Dec. 28, 2006, entitled “TireCompositions And Components Containing Free-Flowing FillerCompositions”.

Application Ser. No. 11/617,678 filed Dec. 28, 2006, entitled “TireCompositions And Components Containing Free-Flowing FillerCompositions”.

Application Ser. No. 11/617,663, filed Dec. 28, 2006, entitled “TireCompositions And Components Containing Silated Core Polysulfides”.

Application Ser. No. 11/617,659, filed Dec. 28, 2006, entitled “TireCompositions And Components Containing Blocked Mercaptosilane CouplingAgent”.

Application Ser. No. 11/647,901, filed Dec. 28, 2006, entitled “SilatedCyclic Core Polysulfides, Their Preparation And Use In Filled ElastomerCompositions”.

Application Ser. No. 11/648,460, filed Dec. 28, 2006, entitled“Free-Flowing Filler Composition And Rubber Composition ContainingSame”.

Application Ser. No. 11/647,903, filed Dec. 28, 2006, entitled“Free-Flowing Filler Composition And Rubber Composition ContainingSame”.

Application Ser. No. 11/648,287, filed Dec. 28, 2006, entitled “SilatedCore Polysulfides, Their Preparation And Use In Filled ElastomerCompositions”.

BACKGROUND OF THE INVENTION

This invention relates to sulfur silane coupling agents containingmultiple blocked mercapto groups which are latent, that is, they are ina state of reduced activity until such a time as one finds it useful toactivate them. The invention also relates to the manufacture of mineralfilled elastomers, rubbers and inorganic fillers comprising these silanecoupling agents, as well as to the manufacture of the silanes.

The majority of art dealing with of sulfur-containing coupling agents inmineral filled elastomers involves silanes containing one or more of thefollowing chemical bond types:

S—H (mercapto), S—S (disulfide or polysulfide), C═S (thiocarbonyl) orC(═O)S (thioester). Mercaptosilanes have high chemical reactivity withorganic polymers used in mineral filled elastomers and therefore effectcoupling at substantially reduced loadings. However, these chemicalbonds between the coupling agent and the organic polymer are weaker thanthe carbon-carbon bonds of the organic polymer. Under high stress and/orhigh frequency use conditions, these chemical bonds are susceptible tobreakage and, therefore, loss of coupling between the organic polymerand the coupling agent. The loss of coupling may contribute to the wearand to the degradation of other elastomeric physical properties. Thehigh chemical reactivity of mercaptosilane coupling agents with organicpolymers also leads to unacceptably high viscosities during processingand premature curing (scorch). Their undesirability is aggravated bytheir odor. As a result, other, less reactive coupling agents such asthe coupling agents that contain the S—S (disulfide and polysulfide),C═S (thiocarbonyl) or C(═O)S (thioester) functional groups are used.Because these silane coupling agents are less reactive with the organicpolymers, they require higher use levels and often do not achieve thesame level of bonding. Similar to the mercaptosilane coupling agents,these sulfur silanes are bonded to the organic polymer through a C—Sbond.

The prior art discloses acylthioalkyl silanes, such asCH₃C(═O)S(CH₂)₁₋₃Si(OR)₃ (M. G. Voronkov et al. in Inst. Org. Khim.,Irkutsk, Russia) and HOC(═O)CH₂CH₂C(═O)S(CH₂)₃Si(OC₂H₅)₃ (U.S. Pat. No.3,922,436 to R. Bell et al.). Takeshita and Sugawara disclosed inJapanese Patent JP 63270751 A2 the use of compounds represented by thegeneral formula CH₂═C(CH₃)C(═O)S(CH₂)₁₋₆Si(OCH₃)₃ in tire treadcompositions; but these compounds are not desirable because theunsaturation α,β to the carbonyl group of the thioester has theundesirable potential to polymerize during the compounding process orduring storage. Prior art by Yves Bomal and Olivier Durel in AustralianPatent AU-A-10082/97 discloses the use in rubber of silanes of thestructure represented by R¹ _(n)X_(3-n)Si-(Alk)_(m)(Ar)_(p)—S(C═O)—R(Formula 1P) where R¹ is phenyl or alkyl; X is halogen, alkoxy,cycloalkoxy, acyloxy, or OH; Alk is alkyl; Ar is aryl; R is alkyl,alkenyl, or aryl; n is 0 to 2; and m and p are each 0 or 1, but not bothzero. This prior art, however, stipulates that compositions of thestructures of Formula (1P) must be used in conjunction withfunctionalized siloxanes. The prior art does not disclose or suggest theuse of compounds of Formula (1P) as latent mercaptosilane couplingagents, nor does it disclose or suggest the use of these compounds inany way that would give rise to the advantages of using them as a sourceof latent mercaptosilane. In addition, these patents do not describecoupling agent that have multiple thioester groups in the appropriatestereochemical configuration to foster multiple linkages to the organicpolymer.

U.S. Pat. Nos. 6,608,125; 6,683,135; 620,439; 6,127,468; 6,777,569;6,528,673 and 6,649,684, US Patent Publication Nos. US20050009955A1,20040220307A1, 2003020900A1, 20030130388A1, and application Ser. Nos.11/105,916 and 10/128,804, and European patent application EP1270657A1teach the use of blocked mercaptosilanes of the structure represented by[[(ROC(═O))_(p)-(G)_(j)]_(k)-Y—S]_(r)-G-(SiX₃)_(s), where Y is apolyvalent blocking group (Q)_(z)A(=E) and r is an integer 1 to 3 inrubber compounds and s is preferably 1 to 3, in rubber master batchesand as a surface treatment for mineral fillers and how to manufacturethe silane. Although these patents and patent applications disclosestructures that possess more than one blocked mercapto group, i.e. r=2or 3, they do not teach the specific stereochemical configurations ofthe polyvalent G structure between the silicon atom and theorganofunctional group necessary to achieve the efficient multiplebonding between the coupling agent and the organic polymer.

U.S. Pat. No. 4,519,430 to Ahmad et al. and U.S. Pat. No. 4,184,998 toShippy et al. disclose the blocking of a mercaptosilane with anisocyanate to form a solid which is added to a tire composition, whichmercaptan reacts into the tire during heating, which could happen at anytime during processing since this is a thermal mechanism. The purpose ofthis silane is to avoid the sulfur smell of the mercaptosilane, not toimprove the processing of the tire. Moreover, the isocyanate used hastoxicity issues when used to make the silane and when released duringrubber processing.

U.S. Pat. No. 3,957,718 to Porchet et al. discloses compositionscontaining silica, phenoplasts or aminoplasts, and silanes, such asxanthates, thioxanthates, and dithiocarbamates; however, the prior artdoes not disclose or suggest the use of these silanes as latentmercaptosilane coupling agents, nor does it suggest or disclose theadvantage of using them as a source of latent mercaptosilane.

U.S. Pat. Nos. 6,359,046; 5,663,226; 5,780,531; 5,827,912; 5,977,225;4,709,065; 6,759,545 and WO 2004000930A1 disclose a class of polysulfidesilane coupling agents that contain more than one S—S (disulfide orpolysulfide) functional groups per molecule. However, the multiple S—Slinkages are achieved by separating the functional groups with anorganic hydrocarbon radical. In use, these S—S groups decompose to formsulfur radicals that couple to the polymer, but generate species thatcontain only one sulfur reactive group per silicon atom. Dittrich, etal. in U.S. Pat. Nos. 5,110,969 and 6,268,421 and Weller, et al.,overcame this feature. They disclosed structures that contain more thanone sulfur functional group directly attached to silicon atom through acyclic hydrocarbon radical. The multiple S—S groups were bonded toadjacent carbon atoms and the silicon atoms were directly attached tothe rings through hydrosilation of the alkoxysilane to a vinylcontaining cyclic hydrocarbons. However, these compounds contained ringsof S—S and carbon atoms or were polymeric materials wherein the silylcontaining hydrocarbon radicals were connected through S—S groups. Thesecyclic or polymeric coupling agents were rendered less reactive with theorganic polymers because they contained S—S groups attached directly tosecondary carbons. The attachment of the S—S containing group tosecondary carbon atoms sterically hinder the reaction of the S—S groupsand inhibit their reactions with the organic polymers.

Therefore, a need exists for latent coupling agents that have lowreactivity to affect processing of the mineral filled elastomers orrubbers without scorch and can be activated at the desired time to formmultiple linkages with the organic polymer. These multiple linkagesprovide sufficient bonding so that the loss of coupling between therubber and coupling agent is minimized during high stress or frequencyuse conditions, such as is experienced by tires, without exhibiting thedisadvantages such as described herein.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to the composition, manufacture anduse of blocked mercaptosilane derivatives in which more than onemercapto group is directly linked to the silicon atom throughcarbon-carbon bonds and in which the mercapto group is blocked (“blockedmercaptosilanes”), i.e., the mercapto hydrogen atom is replaced byanother group (hereafter referred to as “blocking group”). Specifically,the silanes of the present invention are blocked mercaptosilanes inwhich the blocking group contains an unsaturated heteroatom or carbonchemically bound directly to sulfur via a single bond. The use of thesesilanes in the manufacture of inorganic filled rubbers is taught whereinthey are deblocked by the use of a deblocking agent during themanufacturing process. The uses of these silanes in the preparation ofmasterbatches and treated fillers and the manufacture of such silanesare taught as well.

More particularly, the present invention is directed to blockedmercaptosilane compositions comprising at least one component having thechemical structure in formula (1) consisting of:[R_(k)—Y—S(CH₂)_(n)]_(r)-G-(CH₂)_(m)—(SiX¹X²X³)  (1)wherein

each occurrence of Y is a polyvalent species (Q)_(z)A(=E), preferablyselected from the group consisting of

—C(═NR¹)—; —SC(═NR¹)—; —SC(═O)—; (—NR¹)C(═O)—; (—NR¹)C(═S)—; —OC(═O)—;—OC(═S)—; —C(═O)—; —SC(═S)—; —C(═S)—; —S(═O)—; —S(═O)₂—; —OS(═O)₂—;(—NR)S(═O)₂—; —SS(═O)—; —OS(═O)—; (—NR¹)S(═O)—; —SS(═O)₂—; (—S)₂P(═O)—;—(—S)P(═O)—; —P(═O)(—)₂; (—S)₂P(═S)—; —(—S)P(═S)—; —P(═S)(—)₂;(—NR¹)₂P(═O)—; (—NR)(—S)P(═O)—; (—O)(—NR¹)P(═O)—; (—O)(—S)P(═O)—;(═O)₂P(═O)—; —(—O)P(═O)—; —(—NR¹)P(═O)—; (—NR¹)₂P(═S)—;(—NR¹)(—S)P(═S)—; (—O)(—NR¹)P(═S)—; (—O)(—S)P(═S)—; (—O)₂P(═S)—;—(—O)P(═S)—; and —(—NR¹)P(═S)—;

wherein each atom (A) attached to the unsaturated heteroatom (E) isattached to the sulfur, which in turn is linked via a group—(CH₂)_(n)G(CH₂)_(m)— to the silicon atom;

each occurrence of R is chosen independently from hydrogen, straight,cyclic, or branched alkyl, alkenyl groups, aryl groups, and aralkylgroups, with each R containing up to about 18 carbon atoms;

each occurrence of R¹ is chosen independently from hydrogen, alkyl,alkenyl, aryl or aralkyl groups with each R¹ containing up to about 18carbon atoms;

each occurrence of G is chosen independently from a group consisting ofa trivalent or polyvalent hydrocarbon group of 3 to 30 carbon atomsderived by substitution of alkane, alkene or aralkane or a trivalent orpolyvalent heterocarbon group of 2 to 29 carbon atoms with the provisothat G contains a cyclic structure (ring);

each occurrence of X¹ is independently selected from the set ofhydrolysable groups group consisting of —Cl, —Br, R¹O—, R¹C(═O)O—, R¹₂C═NO—, R¹ ₂NO— or R₂N—, wherein each R¹ is as above;

each occurrence of X² and X³ are independently chosen from the groupconsisting of the members listed for R¹ and X¹;

each occurrence of Q is selected independently from oxygen, sulfur, or(—NR—);

each occurrence of A is selected independently from carbon, sulfur,phosphorus, or sulfonyl;

each occurrence of E is selected independently from oxygen, sulfur, orNR¹;

k is 1 to 2; m=1 to 5; n=1 to 5; r is 2 to 4; z is 0 to 2; with theproviso that if A is phosphorus, then k is 2.

In another embodiment, the present invention is directed to a processfor the preparation of the blocked mercaptosilane comprising reacting athioacid with a silylated hydrocarbon containing r terminalcarbon-carbon double bonds.

In another embodiment, the present invention is directed to a processfor the preparation of the blocked mercaptosilane comprising reacting asalt of a thioacid with a silane containing r haloalkyl groups, whereinthe halogen is attached to a primary carbon atom.

In still another embodiment, the present invention is directed to filledelastomer or rubber compound comprising the blocked mercaptosilanes ofthe present invention.

In another embodiment, the present invention is directed to a treatedfiller in which the treated filler comprises the blocked mercaptosilaneof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Silane Structures

The novel blocked mercaptosilanes of the present invention can berepresented by the Formula (1):[R_(k)—Y—S(CH₂)_(n)]_(r)-G-(CH₂)_(m)—(SiX¹X²X³)  (1)wherein

each occurrence of Y is a polyvalent species (Q)_(z)A(=E), preferablyselected from the group consisting of

—C(═NR¹)—; —SC(═NR¹)—; —SC(═O)—; (—NR¹)C(═O)—; (—NR¹)C(═S)—; —OC(═O)—;—OC(═S)—; —C(═O)—; —SC(═S)—; —C(═S)—; —S(═O)—; —S(═O)₂—; —OS(═O)₂—;(—NR)S(═O)₂—; —SS(═O)—; —OS(═O)—; (—NR¹)S(═O)—; —SS(═O)₂—; (—S)₂P(═O)—;—(—S)P)—(═O)—; —P(═O)(—)₂; (—S)₂P(═S)—; —(—S)P(═S)—; —P(═S)(—)₂;(—NR¹)₂P(═O)—; (—NR)(—S)P(═O)—; (—O)(—NR¹)P(═O)—; (—O)(—S)P(═O)—;(—O)₂P(═O)—; —(—O)P(═O)—; —(—NR¹)P(═O)—; (—NR¹)₂P(═S)—;(—NR¹)(—S)P(═S)—; (—O)(—NR¹)P(═S)—; (—O)(—S)P(═S)—; (—O)₂P(═S)—;—(—O)P(═S)—; and —(—NR¹)P(═S)—;

wherein each atom (A) attached to the unsaturated heteroatom (E) isattached to the sulfur, which in turn is linked via a group—(CH₂)_(n)G(CH₂)_(m)— to the silicon atom;

each occurrence of R is chosen independently from hydrogen, straight,cyclic, or branched alkyl, alkenyl groups, aryl groups, and aralkylgroups, with each R containing from 1 to 18 carbon atoms;

each occurrence of R¹ is chosen independently from hydrogen, alkyl,alkenyl, aryl or aralkyl groups with each R¹ containing from 1 to 18carbon atoms;

each occurrence of G is chosen independently form a group consisting ofa trivalent or polyvalent hydrocarbon group of 3 to 30 carbon atomsderived by substitution of alkane, alkene or aralkane or a trivalent orpolyvalent heterocarbon group of 2 to 29 carbon atoms with the provisothat G contains a cyclic structure (ring);

each occurrence of X¹ is independently selected from the set ofhydrolysable groups consisting of —Cl, —Br, R¹O—, R¹C(═O)O—, R¹ ₂C═NO—,R¹ ₂NO— or R₂N—, wherein each R¹ is as above;

each occurrence of X² and X³ are independently chosen from the groupconsisting of the members listed for R¹ and X¹;

each occurrence of Q is selected independently from oxygen, sulfur, or(—NR—);

each occurrence of A is selected independently from carbon, sulfur,phosphorus, or sulfonyl;

each occurrence of E is selected independently from oxygen, sulfur, orNR¹;

k is 1 to 2; m=1 to 5; n=1 to 5; r is 2 to 4; z is 0 to 2; with theproviso that if A is phosphorus, then k is 2.

The term, “heterocarbon”, as used herein, refers to any hydrocarbonstructure in which the carbon-carbon bonding in the backbone isinterrupted by bonding to atoms of nitrogen, and/or oxygen; or in whichthe carbon-carbon bonding in the backbone is interrupted by bonding togroups of atoms containing nitrogen and/or oxygen, such as cyanurate(C₃N₃). Heterocarbon groups also refer to any hydrocarbon in which ahydrogen or two or more hydrogens bonded to carbon are replace with aoxygen or nitrogen atom, such as a primary amine (—NH₂), and oxo (═O).Thus, G includes, but is not limited to branched, straight-chainhydrocarbon containing at least one ring structure, cyclic, and/orpolycyclic aliphatic hydrocarbons, optionally containing etherfunctionality via oxygen atoms each of which is bound to two separatecarbon atoms, tertiary amine functionality via nitrogen atoms each ofwhich is bound to three separate carbon atoms, and/or cyanurate (C₃N₃)groups; aromatic hydrocarbons; and arenes derived by substitution of theaforementioned aromatics with branched or straight chain alkyl, alkenyl,alkynyl, aryl and/or aralkyl groups.

As used herein, “alkyl” includes straight, branched and cyclic alkylgroups; “alkenyl” includes any straight, branched, or cyclic alkenylgroup containing one or more carbon-carbon double bonds, where the pointof substitution can be either at a carbon-carbon double bond orelsewhere in the group; and “alkynyl” includes any straight, branched,or cyclic alkynyl group containing one or more carbon-carbon triplebonds and optionally also one or more carbon-carbon double bonds aswell, where the point of substitution can be either at a carbon-carbontriple bond, a carbon-carbon double bond, or elsewhere in the group.Specific examples of alkyls include methyl, ethyl, propyl, isobutyl.Specific examples of alkenyls include vinyl, propenyl, allyl, methallyl,ethylidenyl norbornane, ethylidene norbomyl, ethylidenyl norbomene, andethylidene norbornenyl. Specific examples of alkynyls includeacetylenyl, propargyl, and methylacetylenyl.

As used herein, “aryl” includes any aromatic hydrocarbon from which onehydrogen atom has been removed; “aralkyl” includes any of theaforementioned alkyl groups in which one or more hydrogen atoms havebeen substituted by the same number of like and/or different aryl (asdefined herein) substituents; and “arenyl” includes any of theaforementioned aryl groups in which one or more hydrogen atoms have beensubstituted by the same number of like and/or different alkyl (asdefined herein) substituents. Specific examples of aryls include phenyland naphthalenyl. Specific examples of aralkyls include benzyl andphenethyl. Specific examples of arenyls include tolyl and xylyl.

As used herein, “cyclic alkyl”, “cyclic alkenyl”, and cyclic alkynylalso include bicyclic, tricyclic, and higher cyclic structures, as wellas the aforementioned cyclic structures further substituted with alkyl,alkenyl, and/or alkynyl groups. Representative examples includenorbomyl, norbornenyl, ethylnorbornyl, ethylnorbornenyl,ethylcyclohexyl, ethylcyclohexenyl, cyclohexylcyclohexyl, andcyclododecatrienyl.

Representative examples of the functional groups (—YS—) present in thesilanes of the present invention include thiocarboxylate ester, —C(═O)S—(any silane with this functional group is a “thiocarboxylate estersilane”); dithiocarboxylate, —C(═S)S— (any silane with this functionalgroup is a “dithiocarboxylate ester silane”); thiocarbonate ester,—OC(═O)S— (any silane with this functional group is a “thiocarbonateester silane”); dithiocarbonate ester, —SC(═O)S— and —OC(═S)S— (anysilane with this functional groups is a “dithiocarbonate ester silane”);trithiocarbonate ester, —SC(═S)S— (any silane with this functional groupis a “trithiocarbonate ester silane”); dithiocarbamate ester,(—N—)C(═S)S— (any silane with this functional group is a“dithiocarbamate ester silane”); thiosulfonate ester, —S(═O)₂S— (anysilane with this functional group is a “thiosulfonate ester silane”);thiosulfate ester, —OS(═O)₂S— (any silane with this functional group isa “thiosulfate ester silane”); thiosulfamate ester, (—N—)S(═O)₂S— (anysilane with this functional group is a “thiosulfamate ester silane”);thiosulfinate ester, —S(═O)S— (any silane with this functional group isa “thiosulfinate ester silane”); thiosulfite ester, —OS(═O)S— (anysilane with this functional group is a “thiosulfite ester silane”);thiosulfimate ester, (—N—)S(═O)S— (any silane with this functional groupis a “thiosulfimate ester silane”); thiophosphate ester, P(═O)(O—)₂(S—)(any silane with this functional group is a “thiophosphate estersilane”); dithiophosphate ester, P(═O)(O—)(S—)₂ or P(═S)(O—)₂(S—) (anysilane with this functional group is a “dithiophosphate ester silane”);trithiophosphate ester, P(═O)(S—)₃ or P(═S)(O—)(S—)₂ (any silane withthis functional group is a “trithiophosphate ester silane”);tetrathiophosphate ester P(═S)(S—)₃ (any silane with this functionalgroup is a “tetrathiophosphate ester silane”); thiophosphamate ester,—P(═O)(—N—)(S—) (any silane with this functional group is a“thiophosphamate ester silane”); dithiophosphamate ester,—P(═S)(—N—)(S—) (any silane with this functional group is a“dithiophosphamate ester silane”); thiophosphoramidate ester,(—N—)P(═O)(O—)(S—) (any silane with this functional group is a“thiophosphoramidate ester silane”); dithiophosphoramidate ester,(—N—)P(═O)(S—)₂ or (—N—)P(═S)(O—)(S—) (any silane with this functionalgroup is a “dithiophosphoramidate ester silane”); trithiophosphoramidateester, (—N—)P(═S)(S—)₂ (any silane with this functional group is a“trithiophosphoramidate ester silane”).

Representative examples of X¹ include methoxy, ethoxy, propoxy,isopropoxy, butoxy, phenoxy, benzyloxy, hydroxy, chloro, and acetoxy.Representative examples of X² and X³ include the representative exampleslisted above for X¹ as well as methyl, ethyl, propyl, isopropyl,sec-butyl, phenyl, vinyl, cyclohexyl, and higher straight-chain alkyl,such as butyl, hexyl, octyl, lauryl, and octadecyl.

Representative examples of trisubstutitued G include any of thestructures derivable from vinylnorbornene and vinylcyclohexene, such as—CH₂CH₂-norbomyl=, —CH(CH₃)-norbornyl=, —CH₂(CH—)-norbornyl-,—CH₂CH₂-cyclohexyl=, —CH(CH₃)-cyclohexyl=, and —CH₂(CH—)-cyclohexyl-;any of the structures derivable from limonene, such as—CH₂CH(CH₃)[(4-methyl-1-C₆H₈═)CH₃], —C(CH₃)₂[(4-methyl-1-C₆H₈═)CH₃], and—CH₂(C—)(CH₃)[(4-methyl-1-C₆H₉—)CH₃], where the notation C₆H9 denotesisomers of the trisubstituted cyclohexane ring lacking substitution inthe 2 position and where C₆H₈ denotes the 1,4 disubstituted cyclohexenering; any of the vinyl-containing structures derivable fromtrivinylcyclohexane, such as —CH₂(CH—)(vinylC₆H₉)CH₂CH₂— and—CH₂(CH—)(vinylC₆H₉)CH(CH₃)—; any of the structures derivable fromtrivinylcyclohexane, such as (—CH₂CH₂)₃C₆H₉, (—CH₂CH₂)₂C₆H₉CH(CH₃)—,—CH₂CH₂C₆H₉[CH(CH₃)—]₂, and C₆H₉[CH(CH₃)—]₃, where the notation C₆H₉denotes any isomer of the trisubstituted cyclohexane ring; any structurederivable by trisubstitution of cyclopentane, tetrahydrocyclopentadiene,cyclohexane, cyclodecane, cyclododecane, any of the cyclododecenes, anyof the cyclododecadienes, cycloheptane, any of the cycloheptenes and anyof the cycloheptadienes; trisubstituted cyanurate, piperazine,cyclohexanone, and cyclohexenone; and any structure derivable bytrisubstituted benzene, tolune, xylene, mesitylene and naphthalene.

Representative examples of tetrasubstituted G include any of thestructures derivable from vinylnorbornene or vinylcyclohexene, such as—CH₂(CH—)-norbornyl= and —CH₂(CH—)-cyclohexyl=; any of the structuresderivable from limonene, such —CH₂(C—)(CH₃)[(4-methyl-1-C₆H₈═)CH₃],where the notation C₆H₈ denotes the 1,4 disubstituted cyclohexene ring;any of the vinyl-containing structures derivable fromtrivinylcyclohexane, such as —CH₂(CH—)(vinylC₆H₉)(CH—)CH₂—, where thenotation C₆H₉ denotes any isomer of the trisubstituted cyclohexane ring;any of the structures derivable from trivinylcyclohexane, such as—CH₂(CH—)C₆H₉[CH(CH₃)—]₂, —CH₂(CH—)C₆H₉[CH₂CH₂—]₂, and—CH₂(CH—)C₆H₉[CH(CH₃)—][CH₂CH₂—], where the notation C₆H₉ denotes anyisomer of the trisubstituted cyclohexane ring; and any structurederivable by tetrasubstitution of cyclopentane,tetrahydrocyclopentadiene, cyclohexane, cyclodecane, cyclododecane, anyof the cyclododecenes, any of the cyclododecadienes, cycloheptane, anyof the cycloheptenes and any of the cycloheptadienes; and any structurederivable by tetrasubstitution of benzene, toluene, xylene, mesityleneand naphthalene.

Representative examples of pentasubstituted G include any of thestructures derivable from trivinylcyclohexane, such as—CH₂CH₂C₆H₉[(CH—)CH₂—]₂, —CH(CH₃)C₆H₉[(CH—)CH₂—]₂, and C₆H₉[(CH—)CH₂—]₃,where the notation C₆H₉ denotes any isomer of the trisubstitutedcyclohexane ring, and any structure derivable by pentasubstitution orhexasubstitution of cyclododecane.

Representative examples of R include hydrogen, methyl, ethyl, propyl,isopropyl, butyl, hexyl, 2-ethylhexyl, octyl, dodecyl, octadecyl,cyclohexyl, phenyl, benzyl, phenethyl, methallyl, and allyl.

In another embodiment of the present invention represented by formula(1) wherein each occurrence of Y is a polyvalent species (Q)_(z)A(=E),each occurrence of Q is independently selected from oxygen, sulfur orNR¹, and A is carbon and E is selected independently from oxygen, sulfuror NR¹. Representative examples are selected from, but not limited to,the group —C(═NR)—; —SC(═NR)—; —NR¹C(═NR¹)—; —C(═O)—; —SC(═O)—;—OC(═O)—; —NR¹C(═O)—; and —C(═S)—; —NR¹C(═S)—; —SC(═S)—.

In another embodiment of the present invention represented by formula(1) Y is —C(═O)—.

In another embodiment of the present invention each occurrence of m is2-4 and n is 1-4.

In another embodiment of the present invention each occurrence of m is2-4 and n is 2-4.

In another embodiment of the present invention each occurrence of m is 2and n is 2.

In another embodiment of the present invention each occurrence of G is asubstituted hydrocarbon containing at least one ring and from 1 to 18carbon atoms.

In another embodiment of the present invention each occurrence of G isselected from the group consisting of substituted cyclopentane,cyclohexane, cycloheptane, cyclooctane, cyclododecane and benzene.

In another embodiment of the present invention each occurrence of the Ris a straight chain alkyl group from 1 to 8 carbon atoms.

In another embodiment of the present invention each occurrence of the Ris selected from the group consisting of hydrogen, methyl, ethyl andpropyl.

In still another embodiment of the present invention the sum of thecarbon atoms within the R groups within the molecule is from 2 to 16,more preferably 6 to 14. This amount of carbon in the R groupfacilitates the dispersion of the inorganic filler into the organicpolymers and can affect the rate of cure, thereby improving the balanceof properties in the cured filled rubber.

In another embodiment of the present invention each occurrence of G isselected from a group consisting of a trisubstituted cyclohexane orbenzene, R is a straight chain alkyl group from 1 to 8 carbon atoms, r=2and m=1 or 2, and n=1 or 2.

Representative examples of the silanes of the present invention include,but are not limited to,1-(2-triethoxysilylethyl)-3,5-bis-(3-thia-4-oxopentyl)benzene,1-(2-triethoxysilylethyl)-3,5-bis-(3-thia-4-oxohexyl)benzene,1-(2-triethoxysilylethyl)-3,5-bis-(3-thia-4-oxoheptyl)benzene,1-(2-tripropoxysilyhnethyl)-3,5-bis-(3-thia-4-oxopentyl)benzene,4-(2triethoxysilylethyl)-1,2-bis-(2-thia-3-oxopentyl)benzene,1-(2-diethoxymethylsilylethyl)-3,5-bis-(3-thia-4-oxopentyl)benzene,4-(2-dimethylethoxysilylethyl)-1,2-bis-(3-thia-4-oxopentyl)benzene,4-(2-triethoxysilylethyl)-1,2-bis-(2-thia-3-oxopentyl)cyclohexane,1-(2-triethoxysilylethyl)-2,4-bis-(2-thia-3-oxopentyl)cyclohexane,2-(2-triethoxysilylethyl)-1,4-bis-(2-thia-3-oxopentyl)cyclohexane,4-(2-diethoxymethylsilylethyl)-1,2-bis-(3-thia-4-oxopentyl)cyclohexane,4-(2-dimethylethoxysilylethyl)-1,2-bis-(3-thia-4-oxopentyl)cyclohexane,4-(2-triethoxysilylethyl)-1,2-bis-(3-thia-4-oxohexyl)cyclohexane,1-(2-triethoxysilylethyl)-2,4-bis-(3-thia-4-oxohexyl)cyclohexane,2-(2-triethoxysilylethyl)-1,4-bis-(3-thia-4-oxohexyl)cyclohexane,4-(2-triethoxysilylethyl)-1,2-bis-(3-thia-4-oxononyl)cyclohexane,1-(2-triethoxysilylethyl)-2,4-bis-(3-thia-4-oxononyl)cyclohexane,2-(2-triethoxysilylethyl)-1,4-bis-(3-thia-4-oxononyl)cyclohexane,4-(2-triethoxysilylethyl)-1,2-bis-(3-thia-4-oxoundecyl)cyclohexane,1-(2-triethoxysilylethyl)-2,4-bis-(3-thia-4-oxoundecyl)cyclohexane,2-(2-triethoxysilylethyl)-1,4-bis-(3-thia-4-oxoundecyl)cyclohexane,4-(2-dimethylethoxysilylethyl)-1,2-bis-(3-thia-4-oxododecyl)cyclohexane,4-(2-triethoxysilylethyl)-1,2-bis-(3-thia-4-oxododecyl)cyclohexane,4-(2-triethoxysilylethyl)-1,2-bis-(3-thia-4-oxo-5-aza-5-methyldodecyl)cyclohexane,(2-triethoxysilylethyl)-1,2-bis-(3,5-dithia-4-oxododecyl)cyclohexane,1-(2-triethoxysilylethyl)-3,5-bis-(3-thia-4-oxopenyl)mesitylene and6-(2-triethoxysilylpropyl)-2,2-bis-(3-thia-4-oxopentyl)cyclohexanone,and mixtures thereof.

In another embodiment mixtures of various blocked mercaptosilanes may beused, including wherein synthetic methods result in a distribution ofvarious silanes or where mixes of blocked mercaptosilanes are used fortheir various blocking or leaving functionalities. Moreover, it isunderstood that the partial hydrolyzates of these blockedmercaptosilanes (i.e., blocked mercaptosiloxanes) may also beencompassed by the blocked mercaptosilanes herein, in that these partialhydrolyzates will be a side product of most methods of manufacture ofthe blocked mercaptosilane or can occur upon storage of the blockedmercaptosilane, especially in humid conditions.

In still another embodiment the silane, if liquid, may be loaded on acarrier, such as a porous polymer, carbon black, siliceous filler, orsilica so that it is in solid form for delivery to the rubber. Thesilane can react with the surface groups of the siliceous filler orsilica, especially if the silane and filler mixture is heated to about50 to 150 degrees C. at atmospheric or reduced pressures.

Manufacture of Silanes

An embodiment of the present invention includes methods for thepreparation of blocked mercaptosilanes which can involve directincorporation of the thioester group into a silane by addition of thethioacid across a carbon-carbon double bond. The reaction is the freeradical addition of a thioacid across a carbon-carbon double bond of analkene-functional silane, catalyzed by UV light, heat, or theappropriate free radical initiator wherein, if the thioacid is athiocarboxylic acid, the two reagents are brought into contact with eachother in such a way as to ensure that whichever reagent is added to theother is reacted substantially before the addition proceeds. Thereaction can be carried out by heating or refluxing a mixture of thealkene-functional silane and the thioacid. Aspects have been disclosedpreviously in U.S. Pat. No. 3,692,812 and by G. A. Gomowicz et al., inJ. Org. Chem. (1968), 33(7), 2918-24. The uncatalyzed reaction can occurat temperatures as low as 105° C., but often fails. The probability ofsuccess increases with temperature and becomes high when the temperatureexceeds 160° C. The reaction may be made reliable and the reactionbrought largely to completion by using UV radiation or a catalyst. Witha catalyst, the reaction can be made to occur at temperatures below 90°C. Appropriate catalysts are free radical initiators, e.g., air,peroxides, preferably organic peroxides, and azo compounds. Examples ofperoxide initiators include peracids, such as perbenzoic and peraceticacids; esters of peracids; hydroperoxides, such as t-butylhydroperoxide; peroxides, such as di-t-butyl peroxide; andperoxy-acetals and ketals, such as 1,1-bis(t-butylperoxy)cyclohexane, orany other peroxide. Examples of azo initiators includeazobisisobutyronitrile (AIBN), 1,1-azobis(cyclohexanecarbonitrile)(VAZO, DuPont product); and azo-tert-butane. The reaction can be run byheating a mixture of the alkene-functional silane and the thioacid withthe catalyst. It is preferable for the overall reaction to be run on anequimolar or near equimolar basis to get the highest conversions. Thereaction is sufficiently exothermic that it tends to lead to a rapidtemperature increase to reflux followed by a vigorous reflux as thereaction initiates and continues rapidly. This vigorous reaction canlead to hazardous boil-avers for larger quantities. Side reactions,contamination, and loss in yield can result as well from uncontrolledreactions. The reaction can be controlled effectively by adding partialquantities of one reagent to the reaction mixture, initiating thereaction with the catalyst, allowing the reaction to run its courselargely to completion, and then adding the remains of the reagent,either as a single addition or as multiple additives. The initialconcentrations and rate of addition and number of subsequent additionsof the deficient reagent depend on the type and amount of catalyst used,the scale of the reaction, the nature of the starting materials, and theability of the apparatus to absorb and dissipate heat. A second way ofcontrolling the reaction would involve the continuous addition of onereagent to the other with concomitant continuous addition of catalyst.Whether continuous or sequential addition is used, the catalyst can beadded alone and/or preblended with one or both reagents or combinationsthereof. Two methods are preferred for reactions involving thioacid,such as thiocarboxylic acid, and alkene-functional silanes containingterminal carbon-carbon double bonds. The first involves initiallybringing the alkene-functional silane to a temperature of 160° to 180°C., or to reflux, whichever temperature is lower. The first portion ofthioacid is added at a rate as to maintain up to a vigorous, butcontrolled, reflux. For alkene-functional silanes with boiling pointsabove 100° to 120° C., this reflux results largely from the relativelylow boiling point of thioacid (88° to 92° C., depending on purity)relative to the temperature of the alkene-functional silane. At thecompletion of the addition, the reflux rate rapidly subsides. It oftenaccelerates again within several minutes, especially if analkene-functional silane with a boiling point above 120° C. is used, asthe reaction initiates. If it does not initiate within 10 to 15 minutes,initiation can be brought about by addition of catalyst. The preferredcatalyst is di-t-butyl peroxide. The appropriate quantity of catalyst isfrom 0.2 to 2 percent, preferably from 0.5 to 1 percent, of the totalmass of mixture to which the catalyst is added. The reaction typicallyinitiates within a few minutes as evidenced by an increase in refluxrate. The reflux temperature gradually increases as the reactionproceeds. Then the next portion of thioacid is added, and theaforementioned sequence of steps is repeated. The preferred number ofthioacid additions for total reaction quantities of about one to aboutfour kilograms is two, with about one-third of the total thioacid usedin the first addition and the remainder in the second. For totalquantities in the range of about four to ten kilograms, a total of threethioacid additions is preferred, the distribution being approximately 20percent of the total used in the first addition, approximately 30percent in the second addition, and the remainder in the third addition.For larger scales involving thioacid and alkene-functional silanes, itis preferable to use more than a total of three thioacid additions and,more preferably, to add the reagents in the reverse order. Initially,the total quantity of thioacid is brought to reflux. This is followed bycontinuous addition of the alkene-functional silane to the thioacid atsuch a rate as to bring about a smooth but vigorous reaction rate. Thecatalyst, preferably di-t-butylperoxide, can be added in small portionsduring the course of the reaction or as a continuous flow. It is best toaccelerate the rate of catalyst addition as the reaction proceeds tocompletion to obtain the highest yields of product for the lowest amountof catalyst required. The total quantity of catalyst used should be 0.5to 2 percent of the total mass of reagents used. Whichever method isused, the reaction is followed up by a vacuum stripping process toremove volatiles and unreacted thioacid and silane. The product may bepurified by distillation.

In another embodiment of the present invention the reaction is betweenan alkali metal salt of a thioacid with a haloalkylsilane. The firststep involves preparation of a salt of the thioacid. Alkali metalderivatives are preferred, with the sodium derivative being mostpreferred. These salts would be prepared as solutions in solvents inwhich the salt is appreciably soluble, but suspensions of the salts assolids in solvents in which the salts are only slightly soluble are alsoa viable option. Alcohols, such as propanol, isopropanol, butanol,isobutanol, and t-butanol, and preferably methanol and ethanol areuseful because the alkali metal salts are slightly soluble in them. Incases where the desired product is an alkoxysilane, it is preferable touse an alcohol corresponding to the silane alkoxy group to preventtransesterification at the silicon ester. Alternatively, nonproticsolvents can be used. Examples of appropriate solvents are ethers orpolyethers such as glyme, diglyme, and dioxanes; N,N-dimethylformamide;N,N-dimethylacetamide; dimethylsulfoxide; N-methylpyrrolidinone; orhexamethylphosphommide. Once a solution, suspension, or combinationthereof of the salt of the thioacid has been prepared, the second stepis to react it with the appropriate haloalkylsilane. This may beaccomplished by stirring a mixture of the haloalkylsilane with thesolution, suspension, or combination thereof of the salt of the thioacidat temperatures corresponding to the liquid range of the solvent for aperiod of time sufficient to complete substantially the reaction.Preferable temperatures are those at which the salt is appreciablysoluble in the solvent and at which the reaction proceeds at anacceptable rate without excessive side reactions. With reactionsstarting from chioroalkylsilanes in which the chlorine atom is notallylic or benzylic, preferable temperatures are in the range of 60° to160° C. Reaction times can range from one or several hours to severaldays. For alcohol solvents where the alcohol contains four carbon atomsor fewer, the most preferred temperature is at or near reflux. Whendiglyme is used as a solvent, the most preferred temperature is in therange of 70° to 120° C., depending on the thioacid salt used. If thehaloalkylsilane is a bromoalkylsilane or a chloroalkylsilane in whichthe chlorine atom is allylic or benzylic, temperature reductions of 30°to 60° C. are appropriate relative to those appropriate for nonbenzylicor nonallylic chloroalkylsilanes because of the greater reactivity ofthe bromo group. Bromoalkylsilanes are preferred over chloroalkylsilanesbecause of their greater reactivity, lower temperatures required, andgreater ease in filtration or centrifugation of the coproduct alkalimetal halide. This preference, however, can be overridden by the lowercost of the chloroalkylsilanes, especially for those containing thehalogen in the allylic or benzylic position. For reactions betweenstraight chain chloroalkylethoxysilanes and sodium thiocarboxylates toform thiocarboxylate ester ethoxysilanes, it is preferable to useethanol at reflux for 10 to 20 hours if 5 to 20 percent mercaptosilaneis acceptable in the product. Otherwise, diglyme would be an excellentchoice, in which the reaction would be run preferably in the range of80° to 120° C. for one to three hours. Upon completion of the reactionthe salts and solvent should be removed, and the product may bedistilled to achieve higher purity.

If the salt of the thioacid to be used is not commercially available,its preparation may be accomplished by one of two methods, describedbelow as Method A and Method B. Method A involves adding the alkalimetal or a base derived from the alkali metal to the thioacid. Thereaction occurs at ambient temperature. Appropriate bases include alkalimetal alkoxides, hydrides, carbonates, and bicarbonates. Solvents, suchas toluene, xylene, benzene, aliphatic hydrocarbons, ethers, andalcohols may be used to prepare the alkali metal derivatives. In MethodB, acid chlorides or acid anhydrides would be converted directly to thesalt of the thioacid by reaction with the alkali metal sulfide orhydrosulfide. Hydrated or partially hydrous alkali metal sulfides orhydrosulfides are available; however, anhydrous or nearly anhydrousalkali metal sulfides or hydrosulfides are preferred. Hydrous materialscan be used, however, but with loss in yield and hydrogen sulfideformation as a coproduct. The reaction involves addition of the acidchloride or acid anhydride to the solution or suspension of the alkalimetal sulfide and/or hydrosulfide and heating at temperatures rangingfrom ambient to the reflux temperature of the solvent for a period oftime sufficient largely to complete the reaction, as evidenced by theformation of the coproduct salts.

If the alkali metal salt of the thioacid is prepared in such a way thatan alcohol is present, either because it was used as a solvent, orbecause it formed, as for example, by the reaction of a thioacid with analkali metal alkoxide, it may be desirable to remove the alcohol if aproduct low in mercaptosilane is desired. In this case, it would benecessary to remove the alcohol prior to reaction of the salt of thethioacid with the haloalkylsilane. This could be done by distillation orevaporation. Alcohols, such as methanol, ethanol, propanol, isopropanol,butanol, isobutanol, and t-butanol are preferably removed by azeotropicdistillation with benzene, toluene, xylene, or aliphatic hydrocarbons.Toluene and xylene are preferred.

Utility

The blocked mercaptosilanes described herein are useful as couplingagents for organic polymers (i.e., rubbers) and inorganic fillers. Theblocked mercaptosilanes are unique in that the high efficiency of themercapto group can be utilized without the detrimental side effectstypically associated with the use of mercaptosilanes, such as highprocessing viscosity, less than desirable filler dispersion, prematurecuring (scorch), and odor. These benefits are accomplished because themercaptan group initially is nonreactive because of the blocking group.The blocking group substantially prevents the silane from coupling tothe organic polymer during the compounding of the rubber. Generally,only the reaction of the silane —SiX¹X²X³ group with the filler canoccur at this stage of the compounding process. Thus, substantialcoupling of the filler to the polymer is precluded during mixing,thereby minimizing the undesirable premature curing (scorch) and theassociated undesirable increase in viscosity. One can achieve bettercured filled rubber properties, such as a balance of high modulus andabrasion resistance, because of the avoidance of premature curing.

The number of methylene groups between the silicon and G group, denotedby m, and sulfur (blocked mercaptan) and G group, denoted by n, improvescoupling because the methylene group mitigates excessive stericinteractions between the silane and the filler and polymer. Twosuccessive methylene groups mitigate steric interactions even furtherand also add flexibility to the chemical structure of the silane,thereby enhancing its ability to accommodate the positional andorientational constraints imposed by the morphologies of the surfaces ofboth the rubber and filler at the interphase, at the molecular level.The silane flexibility becomes increasingly important as the totalnumber of silicon and sulfur atoms bound to G increases from 3 to 4 andbeyond. Tighter structures containing secondary and especially, tertiarycarbon atoms; ring structures; and especially, aromatic structures on Gnear silicon and/or sulfur, are more rigid and cannot readily orient tomeet available binding sites on silica and polymer. This would tend toleave sulfur groups unbound to polymer, thereby reducing the efficiencyby which the principle of multiple bonding of silane to polymer viamultiple blocked mercapto groups on silane, is realized.

The G group from which silicon and blocked mercapto group emanatethrough one or more methylene groups from a cyclic structure alsoimproves coupling because the geometry of the cyclic structure naturallydirects the emanating groups away from each other. This keeps them fromgetting in each other's way and also forces them to orient in divergentdirections, so that silicon can bond to the filler, while sulfur bondsto the polymer phase. Aromatic cyclic structures for G are very rigid.Thus, although they direct silicon and blocked mercapto group indiverging directions, their rigidity limits freedom of orientation. Thealiphatic cyclic G structures, because they do not contain theconjugated double bonds, are more flexible. They combine the advantagesof divergent silicon and sulfur orientations from a cyclic structure andflexibility of the aliphatic cyclic structure.

One embodiment of the present invention is a rubber compositioncomprising:

-   -   a) a blocked mercaptosilane of formula 1;    -   b) an organic polymer;    -   c) a filler; and optionally,    -   d) other additives and curatives.

Another embodiment involves the use of these blocked mercaptosilanes ofthe present invention. One or more of the blocked mercaptosilanes aremixed with the organic polymer before, during, or after the compoundingof the filler into the organic polymer. In a preferred embodiment thesilanes are added before or during the compounding of the filler intothe organic polymer, because these silanes facilitate and improve thedispersion of the filler. The total amount of silane present in theresulting combination should be about 0.05 to about 25 parts by weightper hundred parts by weight of organic polymer (phr), more preferably 1to 10 phr. Fillers can be used in quantities ranging from about 5 to 100phr, more preferably from 25 to 80 phr.

When reaction of the mixture to couple the filler to the polymer isdesired, a deblocking agent is added to the mixture to deblock theblocked mercaptosilane. The deblocking agent may be added at quantitiesranging from about 0.1 to about 5 phr, more preferably in the range offrom 0.5 to 3 phr. If alcohol or water is present (as is common) in themixture, a catalyst (e.g., tertiary amines, Lewis acids, or thiols) maybe used to initiate and promote the loss of the blocking group byhydrolysis or alcoholysis to liberate the corresponding mercaptosilane.Alternatively, the deblocking agent may be a nucleophile containing ahydrogen atom sufficiently labile such that the hydrogen atom could betransferred to the site of the original blocking group to form themercaptosilane. Thus, with a blocking group acceptor molecule, anexchange of hydrogen from the nucleophile would occur with the blockinggroup of the blocked mercaptosilane to form the mercaptosilane and thecorresponding derivative of the nucleophile containing the originalblocking group. This transfer of the blocking group from the silane tothe nucleophile could be driven, for example, by a greater thermodynamicstability of the products (mercaptosilane and nucleophile containing theblocking group) relative to the initial reactants (blockedmercaptosilane and nucleophile). For example, if the nucleophile were anamine containing an N—H bond, transfer of the blocking group from theblocked mercaptosilane would yield the mercaptosilane and one of severalclasses of amides corresponding to the type of blocking group used. Forexample, carboxyl blocking groups deblocked by amines would yieldamides, sulfonyl blocking groups deblocked by amines would yieldsulfonamides, sulfinyl blocking groups deblocked by amines would yieldsulfinamides, phosphonyl blocking groups deblocked by amines would yieldphosphonamides, phosphinyl blocking groups deblocked by amines wouldyield phosphinamides. What is important is that regardless of theblocking group initially present on the blocked mercaptosilane andregardless of the deblocking agent used, the initially substantiallyinactive (from the standpoint of coupling to the organic polymer)blocked mercaptosilane is substantially converted at the desired pointin the rubber compounding procedure to the active mercaptosilane. It isnoted that partial amounts of the nucleophile may be used (i.e., astoichiometric deficiency), if one were to deblock only part of theblocked mercaptosilane to control the degree of vulcanization of aspecific formulation.

Water typically is present on the inorganic filler as a hydrate, orbound to a filler in the form of a hydroxyl group. The deblocking agentcould be added in the curative package or, alternatively, at any otherstage in the compounding process as a single component. Examples ofnucleophiles would include any primary or secondary amines, or aminescontaining C═N double bonds, such as imines or guanidines, with theproviso that said amine contains at least one N—H (nitrogen-hydrogen)bond. Numerous specific examples of guanidines, amines, and imines wellknown in the art, which are useful as components in curatives forrubber, are cited in J. Van Alphen, Rubber Chemicals, (Plastics andRubber Research Institute TNO, Delft, Holland, 1973). Some examplesinclude N,N′-diphenylguanidine, N,N′,N″-triphenylguanidine,N,N′-di-ortho-tolylguanidine, orthobiguanide, hexamethylenetetramine,cyclohexylethylamine, dibutylamine, and 4,4′-diaminodiphenylmethane. Anygeneral acid catalysts used to transesterify esters, such as Bronsted orLewis acids, could be used as catalysts.

The rubber composition need not be, but preferably is, essentially freeof functionalized siloxanes, especially those of the type disclosed inAustralian Patent AU-A-10082/97, which is incorporated herein byreference. Most preferably, the rubber composition is free offunctionalized siloxanes.

In practice, sulfur vulcanized rubber products typically are prepared bythermomechanically mixing rubber and various ingredients in asequentially stepwise manner followed by shaping and curing thecompounded rubber to form a vulcanized product. First, for the aforesaidmixing of the rubber and various ingredients, typically exclusive ofsulfur and sulfur vulcanization accelerators (collectively “curingagents”), the rubber(s) and various rubber compounding ingredientstypically are blended in at least one, and often (in the case of silicafilled low rolling resistance tires) two, preparatory thermomechanicalmixing stage(s) in suitable mixers. Such preparatory mixing is referredto as nonproductive mixing or nonproductive mixing steps or stages. Suchpreparatory mixing usually is conducted at temperatures up to 140° to200° C. and often up to 150° to 180° C. Subsequent to such preparatorymix stages, in a final mixing stage, sometimes referred to as aproductive mix stage, deblocking agent (in the case of this invention),curing agents, and possibly one or more additional ingredients are mixedwith the rubber compound or composition, typically at a temperature in arange of 50° to 130° C., which is a lower temperature than thetemperatures utilized in the preparatory mix stages to prevent or retardpremature curing of the sulfur curable rubber, which is sometimesreferred to as scorching of the rubber composition. The rubber mixture,sometimes referred to as a rubber compound or composition, typically isallowed to cool, sometimes after or during a process intermediate millmixing, between the aforesaid various mixing steps, for example, to atemperature of about 50° C. or lower. When it is desired to mold and tocure the rubber, the rubber is placed into the appropriate mold at aboutat least 130° C. and up to about 200° C., which will cause thevulcanization of the rubber by the mercapto groups on the mercaptosilaneand any other free sulfur sources in the rubber mixture.

By thermomechanical mixing, it is meant that the rubber compound, orcomposition of rubber and rubber compounding ingredients, is mixed in arubber mixture under high shear conditions where it autogenously heatsup as a result of the mixing primarily due to shear and associatedfriction within the rubber mixture in the rubber mixer. Several chemicalreactions may occur at various steps in the mixing and curing processes.

The first reaction is a relatively fast reaction and is consideredherein to take place between the filler and the SiX₃ group of theblocked mercaptosilane. Such reaction may occur at a relatively lowtemperature such as, for example, at about 120° C. The second and thirdreactions are considered herein to be the deblocking of themercaptosilane and the reaction which takes place between the sulfuricpart of the organosilane (after deblocking), and the sulfur vulcanizablerubber at a higher temperature, for example, above about 140° C.

Another sulfur source may be used, for example, in the form of elementalsulfur as S_(g). A sulfur donor is considered herein as a sulfurcontaining compound which liberates free, or elemental, sulfur at atemperature in a range of 140° to 190° C. Examples of such sulfur donorsmay be, but are not limited to, polysulfide vulcanization acceleratorsand organosilane polysulfides with at least two connecting sulfur atomsin its polysulfide bridge. The amount of free sulfur source addition tothe mixture can be controlled or manipulated as a matter of choicerelatively independently from the addition of the aforesaid blockedmercaptosilane. Thus, for example, the independent addition of a sulfursource may be manipulated by the amount of addition thereof and bysequence of addition relative to addition of other ingredients to therubber mixture.

Addition of an alkyl silane to the coupling agent system (blockedmercaptosilane plus additional free sulfur source and/or vulcanizationaccelerator) typically in a mole ratio of alkyl silane to blockedmercaptosilane in a range of 1/50 to ½ promotes an even better controlof rubber composition processing and aging.

In an embodiment of the present invention, a rubber composition isprepared by a process which comprises the sequential steps of:

(A) thermomechanically mixing, in at least one preparatory mixing step,to a temperature of 140° to 200° C., alternatively to 140° to 190° C.,for a total mixing time of 2 to 20 minutes, alternatively 4 to 15minutes, for such mixing step(s);

-   -   (i) 100 parts by weight of at least one sulfur vulcanizable        rubber selected from conjugated diene homopolymers and        copolymers, and copolymers of at least one conjugated diene and        aromatic vinyl compound,    -   (ii) 5 to 100 phr (parts per hundred rubber), preferably 25 to        80 phr, of particulate filler, wherein preferably the filler        contains 1 to 85 weight percent carbon black,    -   (iii) 0.05 to 20 parts by weight filler of at least one blocked        mercaptosilane;

(B) subsequently blending therewith, in a final thermomechanical mixingstep at a temperature to 50° to 130° C. for a time sufficient to blendthe rubber, preferably between 1 to 30 minutes, more preferably 1 to 3minutes, at least one deblocking agent at about 0.05 to 20 parts byweight of the filler and a curing agent at 0 to 5 phr; and optionally

(C) curing said mixture at a temperature of 130° to 200° C. for about 5to 60 minutes.

In another embodiment of the present invention, the process may alsocomprise the additional steps of preparing an assembly of a tire orsulfur vulcanizable rubber with a tread comprised of the rubbercomposition prepared according to this invention and vulcanizing theassembly at a temperature in a range of 130° to 200° C.

Suitable organic polymers and fillers are well known in the art and aredescribed in numerous texts, of which two examples include TheVanderbilt Rubber Handbook, R. F. Ohm, ed. (R. T. Vanderbilt Company,Inc., Norwalk, Conn., 1990), and Manual for the Rubber Industry, T.Kempermann, S. Koch, and J. Sumner, eds. (Bayer A G, Leverkusen,Germany, 1993). Representative examples of suitable polymers includesolution styrene-butadiene rubber (sSBR), styrene-butadiene rubber(SBR), natural rubber (NR), polybutadiene (BR), ethylene-propylene co-and ter-polymers (EP, EPDM), and acrylonitrile-butadiene rubber (NBR).The rubber composition is comprised of at least one diene-basedelastomer, or rubber. Suitable conjugated dienes are isoprene and1,3-butadiene and suitable vinyl aromatic compounds are styrene andalpha methyl styrene. Thus, the rubber is a sulfur curable rubber. Suchdiene based elastomer, or rubber, may be selected, for example, from atleast one of cis-1,4-polyisoprene rubber (natural and/or synthetic, andpreferably natural rubber), emulsion polymerization preparedstyrene/butadiene copolymer rubber, organic solution polymerizationprepared styrene/butadiene rubber, 3,4-polyisoprene rubber,isoprene/butadiene rubber, styrene/isoprene/butadiene terpolymer rubber,cis-1,4-polybutadiene, medium vinyl polybutadiene rubber (35 percent to50 percent vinyl), high vinyl polybutadiene rubber (50 percent to 75percent vinyl), styrene/isoprene copolymers, emulsion polymerizationprepared styrene/butadiene/acrylonitrile terpolymer rubber andbutadiene/acrylonitrile copolymer rubber. An emulsion polymerizationderived styrene/butadiene (eSBR) might be used having a relativelyconventional styrene content of 20 percent to 28 percent bound styreneor, for some applications, an eSBR having a medium to relatively highbound styrene content, namely, a bound styrene content of 30 percent to45 percent. Emulsion polymerization preparedstyrene/butadiene/acrylonitrile terpolymer rubbers containing 2 to 40weight percent bound acrylonitrile in the terpolymer are alsocontemplated as diene based rubbers for use in this invention.

The solution polymerization prepared SBR (sSBR) typically has a boundstyrene content in a range of 5 to 50 percent, preferably 9 to 36percent. Polybutadiene elastomer may be conveniently characterized, forexample, by having at least a 90 weight percent cis-1,4-content.

Representative examples of suitable filler materials include metaloxides, such as silica (pyrogenic and precipitated), titanium dioxide,aluminosilicate and alumina, siliceous materials including clays andtalc, and carbon black. Particulate, precipitated silica is alsosometimes used for such purpose, particularly when the silica is used inconnection with a silane. In some cases, a combination of silica andcarbon black is utilized for reinforcing fillers for various rubberproducts, including treads for tires. Alumina can be used either aloneor in combination with silica. The term “alumina” can be describedherein as aluminum oxide, or Al₂O₃. The fillers may be hydrated or inanhydrous form. Use of alumina in rubber compositions can be shown, forexample, in U.S. Pat. No. 5,116,886 and EP 631,982.

In another embodiment of the present invention, the blockedmercaptosilane may be premixed, or prereacted, with the filler particlesor added to the rubber mix during the rubber and filler processing, ormixing stage. If the silane and filler are added separately to therubber mix during the rubber and filler mixing, or processing stage, itis considered that the blocked mercaptosilane then combines in situ withthe filler.

The vulcanized rubber composition should contain a sufficient amount offiller to contribute a reasonably high modulus and high resistance totear. The combined weight of the filler may be as low as about 5 to 100phr, but is more preferably from 25 phr to 85 phr.

In another embodiment of the present invention, precipitated silicas areused as the filler. The silica may be characterized by having a BETsurface area, as measured using nitrogen gas, preferably in the range of40 to 600 m²/g, and more usually in a range of 50 to 300 m²/g. Thesilica typically may also be characterized by having a dibutylphthalate(DBP) absorption value in a range of 100 to 350, and more usually 150 to300. Further, the silica, as well as the aforesaid alumina andaluminosilicate, may be expected to have a CTAB surface area in a rangeof 100 to 220. The CTAB surface area is the external surface area asevaluated by cetyl trimethylammonium bromide with a pH of 9. The methodis described in ASTM D 3849.

Mercury porosity surface area is the specific surface area determined bymercury porosimetry. For such technique, mercury is penetrated into thepores of the sample after a thermal treatment to remove volatiles. Setup conditions may be suitably described as using a 100 mg sample,removing volatiles during two hours at 105° C. and ambient atmosphericpressure, ambient to 2000 bars pressure measuring range. Such evaluationmay be performed according to the method described in Winslow, Shapiroin ASTM page 39 (1959) or according to DIN 66133. For such anevaluation, a CARLO-ERBA Porosimeter 2000 might be used. The averagemercury porosity specific surface area for the silica should be in arange of 100 to 300 m²/g.

A suitable pore size distribution for the silica, alumina, andaluminosilicate according to such mercury porosity evaluation isconsidered herein to be:

-   5 percent or less of its pores have a diameter of less than about 10    nm; 60 percent to 90 percent of its pores have a diameter of 10 to    100 nm; 10 percent to 30 percent of its pores have a diameter of 100    to 1,000 nm; and 5 percent to 20 percent of its pores have a    diameter of greater than about 1,000 nm.

The silica might be expected to have an average ultimate particle size,for example, in the range of 0.01 to 0.05 μm as determined by theelectron microscope, although the silica particles may be even smaller,or possibly larger, in size. Various commercially available silicas maybe considered for use in this invention such as, from PPG Industriesunder the HI-SIL trademark with designations HI-SIL 210, 243, etc.;silicas available from Rhone-Poulenc, with, for example, designation ofZEOSIL 1165MP; silicas available from Degussa with, for example,designations VN2 and VN3, etc.; and silicas commercially available fromHuber having, for example, a designation of HUBERSIL 8745.

In another embodiment of the present invention, where it is desired forthe rubber composition, which contains both a siliceous filler such assilica, alumina and/or aluminosilicates and also carbon blackreinforcing pigments, to be primarily reinforced with silica as thereinforcing pigment, it is often preferable that the weight ratio ofsuch siliceous fillers to carbon black is at least 3/1 and preferably atleast 10/1 and, thus, in a range of 3/1 to 30/1. The filler may becomprised of 15 to 95 weight percent precipitated silica, alumina,and/or aluminosilicate and, correspondingly 5 to 85 weight percentcarbon black, wherein the carbon black has a CTAB value in a range of 80to 150. Alternatively, the filler can be comprised of 60 to 95 weightpercent of said silica, alumina, and/or aluminosilicate and,correspondingly, 40 to 5 weight percent carbon black. The siliceousfiller and carbon black may be preblended or blended together in themanufacture of the vulcanized rubber.

The rubber composition may be compounded by methods known in the rubbercompounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials.Examples of such commonly used additive materials include curing aids,such as sulfur, activators, retarders and accelerators, processingadditives, such as oils, resins including tackifying resins, silicas,plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes,antioxidants and antiozonants, peptizing agents, and reinforcingmaterials, such as, for example, carbon black. Depending on the intendeduse of the sulfur vulcanizable and sulfur vulcanized material (rubbers),the additives mentioned above are selected and commonly used inconventional amounts.

The vulcanization may be conducted in the presence of an additionalsulfur vulcanizing agent. Examples of suitable sulfur vulcanizing agentsinclude, for example, elemental sulfur (free sulfur) or sulfur donatingvulcanizing agents, for example, an amino disulfide, polymericpolysulfide, or sulfur olefin adducts which are conventionally added inthe final, productive, rubber composition mixing step. The sulfurvulcanizing agents (which are common in the art) are used, or added inthe productive mixing stage, in an amount ranging from 0.4 to 3 phr, oreven, in some circumstances, up to about 8 phr, with a range of from 1.5to 2.5 phr, sometimes from 2 to 2.5 phr, being preferred.

Vulcanization accelerators, i.e., additional sulfur donors, may be usedherein. It is appreciated that they may be, for example, of the typesuch as, for example, benzothiazole, alkyl thiuram disulfide, guanidinederivatives, and thiocarbamates. Representative of such acceleratorsare, for example, but are not limited to, mercapto benzothiazole,tetramethyl thiuram disulfide, benzothiazole disulfide,diphenylguanidine, zinc dithiocarbamate, alkylphenoldisulfide, zincbutyl xanthate, N-dicyclohexyl-2-benzothiazolesulfenamide,N-cyclohexyl-2-benzothiazolesulfenamide,N-oxydiethylenebenzothiazole-2-sulfenamide, N,N-diphenylthiourea,dithiocarbamylsulfenamide, N,N-diisopropylbenzothiozole-2-sulfenamide,zinc-2-mercaptotoluimidazole, dithiobis(N-methyl piperazine),dithiobis(N-beta-hydroxy ethyl piperazine) and dithiobis(dibenzylamine). Other additional sulfur donors, may be, for example, thiuram andmorpholine derivatives. Representative of such donors are, for example,but not limited to, dimorpholine disulfide, dimorpholine tetrasulfide,tetramethyl thiuram tetrasulfide, benzothiazyl-2,N-dithiomorpholide,thioplasts, dipentamethylenethiuram hexasulfide, anddisulfidecaprolactam.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., a primaryaccelerator. Conventionally and preferably, a primary accelerator(s) isused in total amounts ranging from 0.5 to 4 phr, preferably 0.8 to 1.5phr. Combinations of a primary and a secondary accelerator might be usedwith the secondary accelerator being used in smaller amounts (of 0.05 to3 phr) in order to activate and to improve the properties of thevulcanizate. Delayed action accelerators may be used. Vulcanizationretarders might also be used. Suitable types of accelerators are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfonamides,dithiocarbamates, and xanthates. Preferably, the primary accelerator isa sulfenamide. If a second accelerator is used, the secondaryaccelerator is preferably a guanidine, dithiocarbamate, or thiuramcompound.

Typical amounts of tackifier resins, if used, comprise 0.5 to 10 phr,usually 1 to 5 phr. Typical amounts of processing aids comprise 1 to 50phr. Such processing aids include, for example, aromatic, naphthenic,and/or paraffinic processing oils. Typical amounts of antioxidantscomprise 1 to 5 phr. Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others such as those disclosed in theVanderbilt Rubber Handbook (1978), pages 344-46. Typical amounts ofantiozonants comprise 1 to 5 phr. Typical amounts of fatty acids, which,if used, can include stearic acid, comprise 0.5 to 3 phr. Typicalamounts of zinc oxide comprise 2 to 5 phr. Typical amounts of waxescomprise 1 to 5 phr. Often microcrystalline waxes are used. Typicalamounts of peptizers comprise 0.1 to 1 phr. Typical peptizers may be,for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

In still another embodiment of the present invention, the rubbercomposition of this invention can be used for various purposes. Forexample, it can be used for various tire compounds. Such tires can bebuilt, shaped, molded, and cured by various methods which are known andwill be readily apparent to those having skill in such art.

All references cited are incorporated herein as they are relevant to thepresent invention.

The invention may be better understood by reference to the followingexamples in which the parts and percentages are by weight unlessotherwise indicated.

COMPARATIVE EXAMPLE A Preparation of3-(octanoylthio)-1-propyltriethoxysilane

Into a 12-liter, three-necked round bottom flask equipped withmechanical stirrer, addition funnel, thermocouple, heating mantle, N₂inlet, and temperature controller were charged3-mercaptopropyltriethoxysilane (1,021 grams, 3.73 moles purchase asSILQUEST® A-1891 silane from General Electric Company), triethylamine(433 grams), and hexane (3,000 ml). The solution was cooled in an icebath, and octanoyl chloride (693 grams, 4.25 moles) were added over atwo hour period via the addition funnel. After addition of the acidchloride was complete, the mixture was filtered two times, first througha 0.1 μm filter and then through a 0.01 μm filter, using a pressurefilter, to remove the salt. The solvent was removed under vacuum. Theremaining yellow liquid was vacuum distilled to yield 1,349 grams ofoctanoylthiopropyltriethoxysilane as a clear, very light yellow liquid.The yield was 87 percent.

EXAMPLE 1 Preparation of(2-triethoxysilylethyl)-bis-(3-thia-4-oxohexyl)cyclohexane

This example illustrates the preparation of a thiocarboxylatealkoxysilane from a silane containing two vinyl groups through theformation of an intermediate thioacetate silane.

The preparation of the (2-trimethoxysilylethyl)divinylcyclohexane wasprepared by hydrosilation. Into a 5 L, three-neck round bottomed flaskequipped with magnetic stir bar, temperature probe/controller, heatingmantle, addition funnel, condenser, and air inlet were chargedtrivinylcyclohexane (2,001.1 grams, 12.3 moles) and VCAT catalysts (1.96grams, 0.01534 gram platinium). Air was bubbled into the vinyl silane bymeans of the air inlet where the tube was below the surface of thesilane. The reaction mixture was heated to 110° C. and thetrimethoxysilane (1,204 grams, 9.9 moles) was added over a 3.5 hourperiod. The temperature of the reaction mixture increased to a maximumvalue of 130° C. The reaction mixture was cooled to room temperature and1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxylbenzyl)benzene (3grams, 0.004 mole) was added. The reaction mixture was distilled at 122°C. and 1 mmHg pressure to give 1,427 grams of(2-trimethoxysilylethyl)divinylcyclohexane, The yield was 51 percent.

The (2-triethoxysilylethyl)divinylcyclohexane was prepared bytransesterification. Into a 3 L, three-neck round bottomed flaskequipped with magnetic stir bar, temperature probe/controller, heatingmantle, addition funnel, distilling head and condenser, and nitrogeninlet were charged (2-trimethoxysilylethyl)divinylcyclohexane (284grams, 2.33 moles), sodium ethoxide in ethanol (49 grams of 21% sodiumethoxide, purchased from Aldrich Chemical) and ethanol (777 grams, 16.9moles). The reaction mixture was heated and the methanol and ethanolwere removed by distillation at atmospheric pressure. The crude productwas then distilled at 106° C. and under reduced pressure of 0.4 mmHg togive 675 grams of product, 89 percent yield.

The (2-triethoxysilylethyl)bis-(3-thia-4-oxopentyl)cyclohexane wasprepared by addition of thioacetic acid to the divinylsilane. Into a 1L, three-neck round bottomed flask equipped with magnetic stir bar,temperature probe/controller, heating mantle, addition funnel,condenser, air inlet and a sodium hydroxide scrubber, was chargedthioacetic acid (210 grams, 2.71 moles). The(2-triethoxysilylethyl)divinylcyclohexane (400 grams, 1.23 moles) wasadded slowly over a period of 30 minutes and at room temperature bymeans of an addition funnel. The reaction was an exothermic reaction.The temperature of the mixture increased to 94.6° C. The mixture wasstirred for 2.5 hours and allowed to cool to 38.8° C. Additionalthioacetic acid (10 grams, 0.13 moles) was added and a slight exothermalreaction was observed. The reaction mixture was stirred overnight (18hours) at about 25° C. Analysis indicated that the reaction mixturecontained less than 2 percent thioacetic acid. Its overall purity was 91percent. The reaction mixture was further purified by a distillationusing a Kugel apparatus under reduced pressure.

The dimercaptosilane intermediate was prepared by removing the acetylgroups from (2-triethoxysilylethyl)bis-(3-thia-4-oxopentyl)cyclohexane.Into a 5 L, three-neck round bottomed flask equipped with magnetic stirbar, temperature probe/controller, heating mantle, addition funnel,distilling head and condenser, 10-plate Oldershaw column and nitorgeninlet were charged(2-triethoxysilylethyl)bis-(3-thia-4-oxopentyl)cyclohexane (2,000 grams,4.1 moles), ethanol (546.8 grams, 11.8 moles) and sodium ethoxide inethanol (108 grams of a 21% sodium ethoxide in ethanol). The pH of thereaction mixture was about 8. The reaction mixture was heated to 88° C.for 24 hours to remove the ethyl acetate and ethanol from the reactionmixture. Twice ethanol (1 liter) was added to the mixture and the pH ofthe reaction mixture was increase to about 10 by the addition of 21%sodium ethoxide in ethanol (21 grams) and heated an additional 6.5hours. The reaction mixture was cooled and then pressure filtered. Thereaction mixture was stripped at a temperature less than 95° C. and 1mmHg pressure. The stripped product was filtered to give(2-triethoxysilylethyl)bis(2-mercaptoethyl)cyclohexane (1398 grams, 3.5moles, 86% yield).

The (2-triethoxysilylethyl)-bis-(3-thia-4-oxohexyl)cyclohexane wasprepared by the acetylation of the bismercaptosilane. Into a 5 L,three-neck round bottomed flask equipped with magnetic stir bar,temperature probe/controller, ice/water bath, addition funnel andcondenser were charged(2-triethoxysilylethyl)bis(2-mercaptoethyl)cyclohexane (1010.6 grams,2.56 moles), triethylamine (700 grams, 6.93 moles) and methylenechloride (1000 grams). Propionyl chloride (473.8 grams, 5.12 moles) wasadded to the stirred reaction mixture over a 1.5 hour period. Thereaction mixture temperature increased to 50° C. Additional propionylchloride (45.4 grams, 0.49 mole) was added. The reaction mixture wasfiltered and the salts were mixed with 500 mL of methylene chloride andwashed with three times with distilled water and twice with saturatedsodium chloride solution. The organic phase was dried over anhydrousmagnesium sulfate and then stripped at 124° C. and reduced pressure toremove the volatile components. The stripped product (1196 grams, 2.36moles) was analyzed by GC/MS, NMR and LC and the yield was 92 percent.

One isomer of (2-triethoxysilylethyl)-bis-(3-thia-4-oxohexyl)cyclohexanehas the following structure:

EXAMPLE 2 AND 3 The Use of Silanes in Low Rolling Resistant Tire TreadFormulation

A model low rolling resistance passenger tire tread formulation asdescribed in Table 1 and a mix procedure were used to evaluaterepresentative examples of the silanes of the present invention. Thesilane in Example 1 was mixed as follows in a “B” BANBURY (FarrellCorp.) mixer with a 103 cu. in. (1690 cc) chamber volume. The mixing ofthe rubber was done in two steps. The mixer was turned on with the mixerat 80 rpm and the cooling water at 71° C. The rubber polymers were addedto the mixer and ram down mixed for 30 seconds. The silica and the otheringredients in Masterbatch 1 of Table 1 except for the silane and theoils were added to the mixer and ram down mixed for 60 seconds. Themixer speed was reduced to 35 rpm and then the silane and oils of theMaterbatch 1 were added to the mixer and ram down for 60 seconds. Themixer throat was dusted down and the ingredients ram down mixed untilthe temperature reached 149° C. The ingredients were then mixed for anaddition 3 minutes and 30 seconds, The mixer speed was adjusted to holdthe temperature between 152 and 157° C. The rubber was dumped (removedfrom the mixer), a sheet was formed on a roll mill set at about 85° to88° C., and then allowed to cool to ambient temperature.

In the second step, Masterbatch 1 was recharged into the mixer. Themixer's speed was 80 rpm, the cooling water was set at 71° C. and thebatch pressure was set at 6 MPa. The Masterbatch 1 was ram down mixedfor 30 seconds and then the temperature of the Masterbatch 1 was broughtup to 149° C., and then the mixer's speed was reduce to 32 rpm. The zincoxide and stearic acid were added (Masterbatch 2) and the rubber wasmixed for 3 minutes and 20 seconds at temperatures between 152 and 157°C. During this mixing, the trimethylol propane was added (if needed).After mixing, the rubber was dumped (removed from the mixer), a sheetwas formed on a roll mill set at about 85° to 88° C., and then allowedto cool to ambient temperature.

The rubber masterbatch and the curatives were mixed on a 15 cm×33 cm tworoll mill that was heated to between 48° and 52° C. The sulfur andaccelerators were added to the rubber (Masterbatches 1 &2) andthoroughly mixed on the roll mill and allowed to form a sheet. The sheetwas cooled to ambient conditions for 24 hours before it was cured. Thecuring condition was 160° C. for 20 minutes.

Silane from Example 1 was compounded into the tire tread formulationaccording to the above procedure. The performance of the silanesprepared in Examples 1 was compared to the performance of silanes whichare practiced in the prior art, bis-(3-triethoxysilyl-1-propyl)disulfide(TESPD), and Comparative Example A. The test procedures were describedin the following ASTM methods:

Mooney Scorch ASTM D1646 Mooney Viscosity ASTM D1646 Oscillating DiscRheometer (ODR) ASTM D2084 Storage Modulus, Loss Modulus, ASTM D412 andD224 Tensile and Elongation DIN Abrasion DIN Procedure 53516 HeatBuildup ASTM D623 Percent Permanent Set ASTM D623 Shore A Hardness ASTMD2240

The results of this procedure are tabulated below in Table 1.

TABLE 1 Example Number Comp. Comp. Example Example Ingredients Units B C2.00 3.00 Masterbatch 1 SMR-10, natural rubber phr 10.00 10.00 10.0010.00 Budene 1207, polybutadiene phr 35.00 35.00 35.00 35.00 Buna VSL5025-1, oil-ext. sSBR phr 75.63 75.63 75.63 75.63 N339, carbon black phr12.00 12.00 12.00 12.00 Ultrasil VN3 GR, silica phr 85.00 85.00 85.0085.00 Sundex 8125TN, process oil. phr 6.37 6.37 6.37 6.37 Erucical H102,rapeseed oil phr 5.00 5.00 5.00 5.00 Flexzone 7P, antiozonant phr 2.002.00 2.00 2.00 TMQ phr 2.00 2.00 2.00 2.00 Sunproof Improved, wax phr2.50 2.50 2.50 2.50 Kadox 720 C, zinc oxide phr — — — — Industrene R,stearic acid phr — — — — Aktiplast ST, disperser phr 4.00 4.00 4.00 4.00Silane TESPD phr 4.50 — — — Silane Comparative Example 1 phr — 6.90 — —Silane Example 2 phr — — 9.68 9.68 TMP phr 2.50 2.50 2.50 — Masterbatch2 Kadox 720 C, zinc oxide phr 2.50 2.50 2.50 2.50 Industrene R, stearicacid phr 1.00 1.00 1.00 1.00 TMP phr — — — 2.50 Catalysts Naugex MBT0.10 0.10 0.10 0.10 Diphenyl guanidine 2.00 2.00 2.00 2.00 Delac S, CBS2.00 2.00 2.00 2.00 Rubbermakers sulfur 167 2.20 2.20 2.20 2.20 totalphr 256.30 258.69 261.47 261.47 Specific Gravity g/cm3 1.21 1.21 1.221.21 Physical Properties Mooney Viscosity at 100 Celsius mooney units69.60 55.80 55.90 52.70 ML1 + 3 Minimum Torque (Mooney Low) dNm 2.671.74 1.83 1.79 Maximum Torque (Mooney High) dNm 19.31 18.17 19.89 19.40Torque (Max − Min) dNm 16.64 16.43 18.06 17.61 1.13 DNM RISE min 1.301.50 1.15 0.98 2.26 DNM RISE min 1.77 1.78 1.40 1.18 Cure, 160 Celsiusfor 20 minutes T-10 min 1.65 1.70 1.37 1.15 T-40 min 2.50 2.27 2.01 1.65T-95 min 13.36 15.00 19.80 17.62 cure time min 20.00 20.00 20.00 20.00 50% Modulus MPa 1.40 1.57 1.57 1.50 100% Modulus MPa 2.53 2.83 2.802.80 300% Modulus MPa 12.20 11.87 12.23 12.80 Reinforcement Index 4.824.19 4.37 4.57 Tensile MPa 16.80 15.30 15.93 17.13 Elongation % 425.20406.40 410.40 416.90 M300 − M100 9.67 9.04 9.43 10.00 Durometer Shore“A” shore A 66.80 67.90 68.90 68.50 Zwick Rebound, Room Temperaturepercent 30.50 33.60 30.10 30.90 Zwick Rebound, 70 Celsius percent 47.7049.70 49.90 49.60 Delta Rebound, 70 C. - RT percent 17.20 16.10 19.8018.70

The data from Table 1 show an improvement in the delta rebound, anindicator of improve traction, and torque, an indicator of improvedwear, while maintaining the other processing and physical propertieswhen trimethylol propane was added as an activator.

EXAMPLES 4 AND 5

The rubber compounds described in Table 2 were prepared according to theprocedures of Examples 2 and 3. The data from Table 2 show and improvein the delta rebound over the two comparative Example D and E.

TABLE 2 Example Number Comp. Comp. Example Example Ingredients Units D E4.00 5.00 Masterbatch 1 SMR-10, natural rubber phr 10.00 10.00 10.0010.00 Budene 1207, polybutadiene phr 35.00 35.00 35.00 35.00 Buna VSL5025-1, oil-extended sSBR phr 75.63 75.63 75.63 75.63 N 339, carbonblack phr 12.00 12.00 12.00 12.00 Ultrasil VN 3 GR, Silica phr 85.0085.00 85.00 85.00 Sundex 8125TN, process oil phr 6.37 6.37 6.37 6.37Erucical H 102, rapeseed oil phr 5.00 5.00 5.00 5.00 Flexzone 7P,antiozonant phr 2.00 2.00 2.00 2.00 TMQ phr 2.00 2.00 2.00 2.00 SunproofImproved, wax phr 2.50 2.50 2.50 2.50 Kadox 720 C, zinc oxide phr — —2.50 — Industrene R, stearic acid phr — — 1.00 — Aktiplast ST, disperserphr 4.00 4.00 4.00 4.00 Silane TESPD phr 4.50 — — — Silane ComparativeExample 1 phr — 6.90 — — Silane Example 2 phr — — 9.68 9.68 TMP phr — —— — Masterbatch 2 Kadox 720 C, zinc oxide phr 2.50 2.50 — 2.50Industrene R, stearic acid phr 1.00 1.00 — 1.00 TMP phr — — — —Catalysts Naugex MBT phr 0.10 0.10 0.10 0.10 Diphenyl guanidine phr 2.002.00 2.00 2.00 Delac S, CBS phr 2.00 2.00 2.00 2.00 Rubbermakers sulfur167 phr 2.20 2.20 2.20 2.20 total phr 253.80 256.20 258.97 258.97Specific Gravity g/cm³ 1.21 1.21 1.21 1.21 Physical Properties MooneyViscosity at 100° Celsius Mooney units 75.50 67.10 61.20 60.60 ML 1 + 3Minimum Torque (Mooney Low) dNm 2.99 2.26 1.96 2.04 Maximum Torque(Mooney High) dNm 18.52 17.40 17.55 17.82 Torque (Max − Min) dNm 15.5315.14 15.59 15.78 1.13 DNM RISE minutes 0.80 1.97 1.39 1.80 2.26 DNMRISE minutes 1.73 2.41 1.76 2.17 Cure, 160° Celsius for 20 minutes T-10minutes 1.41 2.24 1.64 2.05 T-40 minutes 3.09 3.12 2.37 2.81 T-95minutes 11.20 10.87 12.23 12.22 cure time minutes 20.00 20.00 20.0020.00  50% Modulus MPa 1.20 1.33 1.20 1.20 100% Modulus MPa 2.00 2.402.10 2.17 300% Modulus MPa 10.47 11.03 10.53 10.53 Reinforcement Index5.24 4.60 5.01 4.86 Tensile MPa 17.33 16.27 17.23 16.57 Elongation %470.40 446.60 474.00 462.80 M300 − M100 8.47 8.63 8.43 8.36 DurometerShore “A” shore A 62.60 64.40 63.00 64.60 Zwick Rebound, RoomTemperature percent 32.00 35.00 33.20 31.60 Zwick Rebound, 70° Celsiuspercent 47.70 50.40 50.00 48.60 Delta Rebound, 70° C. - RT percent 15.7015.40 16.80 17.00

EXAMPLE 6 Preparation of(2-triethoxysilylethyl-bis-(3-thia-4-oxoundecyl)cyclohexane

This example illustrates the preparation of a thiocarboxylatealkoxysilane from a silane containing two vinyl groups and a thioacid.Into a 3 L, three-neck round bottomed flask equipped with magnetic stirbar, temperature probe/controller, heating mantle, addition funnel,condenser, air inlet and a sodium hydroxide scrubber, was chargedthiooctanoic acid (780.1 grams, 4.87 moles). Air was bubbled into thethioacid by means of the air inlet where the tube was below the surfaceof the thioacid. (2-Triethoxysilylethyl)-divinylcyclohexane (755.0grams, 2.31 moles) was added slowly to the thioacid by means of anaddition funnel over a period of 32 minutes. The addition started at22.3° C. and a slight exothermal reaction occurred which raised thetemperature to 34.9° C. The reaction mixture was then slowly heated to84.8° C. over 3 hours. Di-tert-butyl peroxide (1.1 grams) was added andstirred for 2 hours. 2,2′-Azoisobutyronitrile (1.2 grams, from AldrichChemical) was added and the mixture was heated for an additional 4.4hours at 85° C. The thiooctanoic acid (32.4 grams) was removed underreduced pressure (0.5 mmHg) and elevated temperature of 167° C. to give1,472.1 grams of product. ¹³C NMR analysis indicated that 95% reactionoccurred between the thiooctanoic acid and the vinyl groups of(2-triethoxysilylethyl)divinylcyclohexane.

EXAMPLE 7 Preparation of(2-triethoxysilylethyl-bis(3-thia-4-oxohexyl)cyclohexane

This example illustrates the preparation of a thiocarboxylatealkoxysilane from a silane containing two vinyl groups and a thioacid.Into a 3 L, three-neck round bottomed flask equipped with magnetic stirbar, temperature probe/controller, heating mantle, addition funnel,condenser, air inlet and a sodium hydroxide scrubber, was chargedthiopropanoic acid (591.8 grains, 6.49 moles). Air was bubbled into thethioacid by means of the air inlet where the tube was below the surfaceof the thioacid. (2-Triethoxysilylethyl)-divinylcyclohexane (1052.0grams, 3.22 moles) was added to the thioacid by means of an additionfunnel over a period of 15 minutes. The addition started at 21.0° C. andan exothermic reaction occurred which raised the temperature to 86.7° C.After 70 minutes, the reaction mixture was then heated to maintain atemperature of about 86° C. for an additional 20 minutes.2,2′-Azoisobutyronitrile (1.2 grams, from Aldrich Chemical) was addedand the mixture was heated for one hour at 86° C. Di-tert-butyl peroxide(2.0 grams) was charge to the reaction mixture and heated for 7 hours at86° C. The thiopropanoic acid was removed under reduced pressure (0.5mmHg) and elevated temperature of 70° C. to give the product.

While the above description contains many specifics, these specificsshould not be construed as limitations of the invention, but merely asexemplifications of preferred embodiments thereof. Those skilled in theart will envision many other embodiments within the scope and spirit ofthe invention as defined by the claims appended hereto.

What is claimed is:
 1. A compound having the structure(2-triethoxysilylethyl)bis-(3-thia-4-oxopentyl)cyclohexane.
 2. A methodfor making the compound of claim 1 comprising reacting a thioacetic acidwith (2-triethoxysilylethyl)divinylcyclohexane.
 3. The method of claim1, wherein the reaction is catalyzed by UV radiation.
 4. The method ofclaim 2, wherein the reaction is conducted in the presence of a freeradical initiator.
 5. The method of claim 4, wherein the free radicalinitiator is selected from the group consisting of air, peracid, esterof peracid, peroxide, hydroperoxide, peroxy-acetal, peroxy-ketal,azobisisobutyronitrile, 1,1-azobis(cyclohexanecarbonitrile) andazo-tert-butane.
 6. The method of claim 4, wherein the reaction isconducted at a temperature below 90° C.
 7. A rubber compositionincluding a compound of claim
 1. 8. A rubber composition comprising: (a)a compound of claim 1; (b) an organic polymer; (c) a filler; andoptionally, (d) other additives and curatives.
 9. The rubber compositionof claim 8 wherein the organic polymer (b) is selected from the groupconsisting of solution styrene-butadiene rubber, emulsionstyrene-butadiene rubber, natural rubber, polybutadiene rubber,ethylene-propylene copolymer, ethylene-propylene-diene monomer (EPDM),acrylonitrile-butadiene rubber, cis-1,4-polyisoprene rubber,3,4-polyisoprene rubber, cis-1,4-polybutadiene rubber, medium vinylpolybutadiene rubber, high vinyl polybutadiene rubber, and mixturesthereof.
 10. The rubber composition of claim 8 wherein the filler (c) isselected from the group consisting of pyrogenic silica, precipitatedsilica, titanium dioxide, aluminosilicate, alumina, clay, talc andcarbon black.
 11. A process for preparing a cured rubber compositioncomprising: (A) thermomechanically mixing, in at least one preparatorymixing step, to a temperature of from 140° to 200° C. and for a totalmixing time of 2 to 20 minutes, (i) 100 parts by weight of at least onesulfur vulcanizable rubber selected from conjugated diene homopolymer,conjugated diene copolymer, and copolymer of at least one conjugateddiene and aromatic vinyl compound, (ii) 5 to 100 parts per hundredrubber of at least one particulate filler, (iii) 0.05 to 20 parts byweight filler of a compound having the structure of claim 1; (B)subsequently blending therewith, in a final thermomechanical mixing stepat a temperature to 50° to 130° C., the rubber of step (A), at least onedeblocking agent in an amount of from 0.05 to 20 parts by weight of thefiller and a curing agent in an amount of from 0 to 5 parts per hundredparts rubber; and (C) curing said mixture.
 12. The process of claim 11,wherein the particulate filler is selected from the group consisting ofpyrogenic silica, precipitated silica, titanium dioxide,aluminosilicate, alumina, clay, talc and carbon black.
 13. The processof claim 11 wherein the sulfur vulcanizable rubber is selected from thegroup consisting of solution styrene-butadiene rubber, emulsionstyrene-butadiene rubber, natural rubber, polybutadiene rubber,ethylene-propylene copolymer, ethylene-propylene-diene monomer (EPDM),acrylonitrile-butadiene rubber, cis-1,4-polyisoprene rubber,3,4-polyisoprene rubber, cis-1,4-polybutadiene rubber, medium vinylpolybutadiene rubber and high vinyl polybutadiene rubber.
 14. A freeflowing filler composition comprising the compound of claim 1 and atleast one particulate filler.
 15. The free flowing filler composition ofclaim 14 wherein the particulate filler is selected from the groupconsisting of pyrogenic silica, precipitated silica, titanium dioxide,aluminosilicate, alumina, clay, talc and carbon black.